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FLEXO Magazine : January 2009
TECHNOLOGIES & TECHNIQUES FIGURE 1. Spectrophotometric readings of drawdowns of one ink supplier over time. Process Control for the Flexographic Pressroom By Brian Ashe H ow do we define good printing? Some may describe it as printing that is repeatable and predictable or printing that meets or exceeds customer expectations. Most would agree that the best printing is printing that is profitable. These notions are not mutually exclusive and good use of process con- trol is a means to help you achieve both goals. Statistical process control (SPC) can be applied to color control in the flexographic pressroom. To use SPC, the printing process must be monitored and upper/lower limits established to keep the process in compliance with a set of standards. The ultimate goal is to continually narrow these control limits, so as to reduce the range of possible variation. If you are uncertain what the upper and lower control limits of your printing process should be, FIRST (Flexographic Image Reproduction Specifications and Tolerances) is a great place to start (see FLEXOOctober 2008, page 62). Prepress calibration can bring the printing process to a pre- dictable and repeatable state for flexography. Characterization (color management and use of ICC profiling) captures and docu- 20 FLEXO JANUARY 2009 ments this calibration. Process control monitors and keeps the process on track through routine data collection. Depending on the process measured, this could be as simple as a tally sheet, or as sophisticated as in-line color measurement on press. Data col- lection and interpretation is required to achieve success using SPC. An ICC profile is useless without process control—when a press is not stable and predictable, it is impractical to bother with characterization. Process control implies continuous review and improvement. To achieve the desired quality results, you can’t just measure once. When I was a quality manager for a printing company imple- menting a SPC program, one of the main challenges was to get the operators to read and understand the data they were col- lecting during pressruns. Using a scanning spectrophotometer, we were tracking average variations in density. The numbers were generally falling into a range three, four, five, or six points, which reminded me of golf scores. I set up a 72-hole (72 colors of density variation measurements) golf tournament with the com- www. f le xography. org
End of Year 2008